The think-aloud protocol is one of the main techniques used by usability professionals when conducting usability studies. Two of the most common think-aloud protocols that usability practitioners use today are Concurrent Think-Aloud (CTA) and Retrospective Think Aloud (RTA). In this study, we analyzed whether think-aloud condition and age influenced usability measures of accuracy, efficiency, and satisfaction. We also assessed differences and similarities in verbalizations by age and by think-aloud condition. Results show that of the three age groups (young, middle-age, and older adults), only the middle-age adults in the CTA condition showed effects: they were more accurate for the difficult task and took longer to complete the task. Age did not affect satisfaction ratings. CTA led to a higher percentage of present tense, positive, and affective utterances, whereas RTA led to a higher percentage of past tense, insight and cognitive utterances. The differences in performance by age and think-aloud protocol highlight the importance of including demographic characteristics such as age when reporting results of usability testing. Depending on the goals of the usability study, a researcher might opt to use CTA when interested in obtaining a real sense of the users' experience with the interface. Conversely, if the researcher is interested in gaining a user's insight into what the issues are with a user interface, he/she might opt to do an RTA study.
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